1. Field of the Invention
The present invention relates to a catalyst useful for the polymerization of olefins, the preparation thereof, and to a process for polymerizing olefins using said catalyst.
2. Description of Prior Art
Heretofore, it has been well-known that Ziegler catalysts, which are combinations of transition metal compounds of Groups IVa-VIa of the Periodic Table, and organo-metallic compounds of Groups IA-III of the Periodic Table, are quite useful for the polymerizaton of olefins, such as ethylene. However, conventional catalysts do not possess satisfactorily high catalytic activity and are not entirely industrially acceptable. Moreover, it has been difficult to use the resulting polymers without removal of catalytic residue following polymerization.
When polyethylene is prepared by slurry polymerization, at temperatures of below that at which the polymer dissolves in a hydrocarbon, such as 90.degree. C, to obtain the polymer in the form of a powder, the bulk density of the resulting polyethylene powder will affect the productivity of the polyethylene. The known catalysts do not produce satisfactory results.
It has also been known to prepare a Ziegler catalyst having high catalytic activity by supporting a transition metal compound on a solid support containing a Group II element of the Periodic Table, especially Mg. Catalysts comprising a chloride of a transition metal, such as titanium supported on a carrier of magnesium chloride, or a compound derived from magnesium chloride which bear close relationship to the present invention, have been disclosed in Japanese Patent Publication No. 12105/1964 (U.S. Pat. No. 3,238,146); Japanese Patent Publication No. 34092/1971 (U.S. Pat. No. 3,642,746); Japanese Patent Publication No. 41670/1972 (Great Britain Pat. No. 1,286,867); and Japanese Patent Publication No. 46269/1972 (Great Britain Pat. No. 1,292,853). In these catalysts, transition metal compounds have been effectively utilized so that the catalytic activity of the transition metal per se has been quite improved. However, even with a carrier, the catalytic activity of conventional catalysts of this type has not been completely satisfactory.
Moreover, when the olefin being polymerized is ethylene, the distribution of the molecular weight of the resulting polyethylene is not satisfactorily narrow.
In the processes disclosed in the prior art, transition metal compounds, in vapor, liquid or solid form, are contacted with solid carriers, which have desirable characteristic features, e.g., appropriate physical properties or formulation properties. Accordingly, the dispersibility of the transition metal compound has been limited because the solid is used as one component. On the other hand, it has been known that liquid magnesium compounds can be used as reducing agents and liquid transition metal compounds contacted therewith. For example, in Japanese Patent Publication No. 40959/1972, a process is disclosed providing a solid catalyst prepared by reducing a transition metal compound having normal or maximum valency, such as TiCl.sub.4, with RMg(OR') (R and R' represent hydrocarbon residues). The catalytic activity of the resulting catalyst is relatively higher than those of the transition metal compounds having lower valency prepared by reduction with a conventional organo-aluminum compound. However, it is still not sufficient to attain the desired purpose.
As stated above, Ziegler-Natta type catalysts having a metal compound of Group II (mainly Mg) as one component are classified into (1) catalysts prepared by contacting a solid magnesium compound with a transition metal compound, and (2) catalysts prepared by contacting a liquid magnesium compound reducing agent with a transition metal compound. However, the objects of this invention have not been attained by using either of these catalysts. The reason may be as follows: In the former, the transition metal compound is not uniformly dispersed into the solid magnesium compound carrier. In the latter, the amount of the magnesium compound combined with the solid transition metal compound having lower valency is stoichiometrically limited. That is, it is impossible to prepare a solid containing sufficient magnesium, which can be uniformly dispersed throughout the transition metal compound. From the above-mentioned viewpoints, the present invention have proposed in the past, that solid catalysts having the formula (Ti.sub.m.V.sub.1-m) X.sub.3.nY (m&lt;1; X: a halogen; Y :ether) prepared by precipitating a reaction product from an ether solution of two transition metal complexes TiX.sub.3.n'Y and VX.sub.3.sub.' n"Y, are effective as catalysts for the polymerization of an olefin (Japanese Patent Application No. 82842/1973). However, it would be most desirable to have additional catalysts with superior effectiveness for polymerization of olefins which are free from the above-described disadvantages.